A hydroelectric power device is known which utilizes a weir in the middle of a waterway to cause water to descend and generate a small amount of hydroelectric power from this descent (for example, see Patent Document 1).
This prior art hydroelectric power device is made by providing an L-shaped draft tube inside the waterway on the upstream side of the weir plate. A waterwheel is installed in the draft tube such that the waterwheel is rotated by the water flow inside the draft tube, and a generator is driven by the waterwheel.    Patent Document 1: Unexamined Japanese Patent Bulletin No. H11[1999]-30179